1. Field of the Invention
The present invention relates to a lead frame for use in a semiconductor device.
2. Description of the Background Art
Hitherto, it has been popular to use a QFP (Quad Flat Package) type semiconductor device in which external leads are arranged on four sides of a semiconductor device using a lead frame as a wiring base member. Recently, under the background of high density integration of semiconductor chips, multiple pins are arranged in the semiconductor device, and instead of the QFP type semiconductor device, a ball grid array (Ball Grid Array, hereinafter referred to as BGA) type semiconductor device in which external leads are arranged over a surface, and a non lead (Quad Non Lead Package, hereinafter referred to as QFN) type semiconductor device have been increasingly used. Generally, in the BGA type semiconductor device, a printed circuit board is popularly used as a wiring base member. However, in such a conventional BGA type semiconductor device, a wiring line is connected by way of a through hole, which is a high-priced structure. Therefore, recently a BGA type semiconductor device and a QFN type semiconductor device using a low-priced lead frame as a wiring base member have been put into practical use.
A semiconductor device using a conventional lead frame a wiring base member is hereinafter described with reference to the accompanying drawings. FIG. 9A is a sectional view showing a construction of a conventional BGA type semiconductor device disclosed in the Japanese Laid-Open Patent Publication (unexamined) No. Hei. 11-74404, and FIG. 9B is a bottom view of the semiconductor device shown in FIG. 9A. FIG. 10A is a plan view showing a lead frame used in the conventional BGA type semiconductor device and arranged in a single line. FIG. 10B is a sectional view taken along the line Xbxe2x80x94Xb indicated by the arrows in FIG. 10A. FIG. 10C is a sectional view taken along the line Xcxe2x80x94Xc indicated by the arrows in FIG. 10A.
In FIGS. 9A, 9B, 10A, 10B and 10C, the conventional BGA type semiconductor device uses a lead frame 50 as a wiring base member, and a semiconductor chip 1 provided with a pad electrode is mounted on a die pad 2 with a junction material 3. The semiconductor device has a soldering ball mounting portion (hereinafter referred to as external electrode portion) 4. A lead electrode 5 of which an inside end portion is arranged proximate the die pad 2 and a pad electrode of the semiconductor chip 1 are connected to each other through a connecting lead 6 and sealed with a resin layer 7. Portions 4a and 4b continued underneath the lead electrode 5 are made thin by etching, except the external electrode portion 4. Accordingly, the die pad 2, the external electrode portion 4 and a suspension lead 8 for supporting the die pad 2 are exposed on the same surface as the under surface of the resin layer 7. A soldering ball 9 is mounted on the external electrode portion 4, and an end of the lead electrode 5 and that of the suspension lead 8 are finally cut along the resin seal line 7a. 
A manufacturing method is hereinafter described with reference to FIGS. 9 to 11C. FIGS. 11A, 11B and 11C are explanatory views showing a manufacturing method of the conventional BGA type semiconductor device using a conventional type lead frame as a wiring base member. FIG. 11A is a sectional view of the lead frame shown in FIG. 10C. FIG. 11B is a sectional view showing molds applied at the time of sealing with the resin layer. FIG. 11C is a sectional view showing an assembling step before mounting the soldering ball has completed.
First, the lead frame 50 shown in FIGS. 10A, 10B and 10C is manufactured. More specifically, after forming a resist film not shown on the upper surface 50a and the under surface 50b of the lead frame 50 and patterning it as shown in FIG. 10A, it is etched from the upper surface 50a and the under surface 50b. Thus, the die pad 2, the external electrode portion 4, the lead electrode 5, the suspension lead 8 and a dam bar 50c are formed and continue one another across openings 50d and 50e. Then, after forming a resist film (not shown) on to the under surface 50b side of the lead frame 50, except the portions 4a and 4b on the underside of the lead electrode 5, the portions 4a and 4b are formed by half etching.
Subsequently, the semiconductor chip 1 provided with the pad electrode is mounted on the die pad 2 by applying the junction material 3. The pad electrode of the semiconductor chip 1 and the inside end of the lead electrode 5 are then connected through the connection lead 6. Then, as shown in FIG. 11B, after mounting a lower mold 10 in contact with the die pad 2 and the external electrode portion 4, an upper mold 11 is positioned to the resin seal line 7A and mounted on the upper surface of the lead frame 50. After tightening the two molds 10 and 11, the semiconductor chip 1, the die pad 2, the lead electrode 5 and the connecting lead 6 are sealed with the seal resin layer 7 by transfer molding. Thereafter, when removing the upper mold 11 and the lower mold 10, a non lead type semiconductor device, before mounting the soldering ball 9, is obtained, as shown in FIG. 11C.
Then, by applying a soldering paste to the external electrode portion 4, the soldering ball 9 is mounted on the external electrode portion 4. When the lead electrode 5 protruding from the resin sealing line 7a, and the seal resin layer 7 gets into the underside portions 4a and 4b of the lead electrode 5 that is thin, are cut along the resin seal line 7a with a cutter, the conventional BGA type semiconductor device shown in FIGS. 9A and 9B is obtained.
In the mentioned semiconductor device using the conventional lead frame as the wiring base member, since the die pad 2, the external electrode portion 4, the lead electrode 5, the suspension lead 8 and dam bar 50c are continuous across the openings 50d and 50e, when sealed with the seal resin layer 7 after mounting the two molds 10 and 11, the molten resin having a low viscosity is formed also in the opening portion 50d. As a result, there has been a problem that the resin molten intrudes into a small space between contact surfaces, where the die pad 2, the external electrode portion 4, the suspension lead 8 are in contact with the lower mold 10, and comes to form a thin resin film (hereinafter referred to as thin burr).
It is certainly possible to prevent the thin burr formed between the external electrode portion 4 and the lower mold 10 if contact pressure between the external electrode portion 4 and the lower mold 10 is large. However, the lead electrode 5 is thin and supported like a cantilever at a part held between the lower mold 10 and the upper mold 11 at the position of the resin seal line 7a. Therefore, if the external electrode portion 4 is pressed by the lower mold 10, the lead electrode 5 is deformed by the pressure. As a result, it has been heretofore impossible to secure a contact pressure capable of preventing the formation of the thin burr between the external electrode portion 4 and the lower mold 10.
The formation of the thin burr varies depending on the degree of roughness in surface finishing (hereinafter referred to as surface roughness) of the contact surface where the die pad 2 and the external electrode portion 4 are in contact with the lower mold 10. Generally, the thin burr does not adhere to any die or mold having a good surface roughness, but adheres to the die pad 2, the external electrode portion 4, etc. having poor surface roughness. Therefore, it is necessary to remove the thin burr adhered, for example, to the external electrode portion 4. To remove the thin burr, hydraulic pressure trimming, chemical trimming, chemical and hydraulic pressure trimming, etc. are performed, and after removing the thin burr, it is necessary to perform treatments such as washing, drying, etc., and, as a result, manufacturing cost is high.
There has been another problem that the lead electrode 5 protruding from the resin seal line 7a, the seal resin layer 7 in the portions 4a and 4b made thin by half etching, and the suspension lead 8, are cut using a cutter along the resin seal line 7a. Therefore, it is easy to cause a failure in cutting the portion of the seal resin layer 7 in the portion 4b. As a result, the resin seal a line 7a is not linear but has a complicated crushed configuration, resulting in a defective product.
The present invention was made to solve the above-discussed problems and has an object of providing a lead frame for a semiconductor device capable of preventing the production of a thin burr on the surface of the lead frame in contact with the lower mold, for example, between the die pad or the external electrode portion and the lower mold.
Another object of the invention is to provide a semiconductor device capable of preventing the cutout portion of the seal resin layer of the semiconductor device from having a complicated crushed configuration.
A lead frame for semiconductor device according to the invention includes a plate-like body having an uneven upper surface and a plain under surface, and the plate-like body includes a first thin portion for mounting a semiconductor chip provided with a plurality of pad electrodes, a plurality of first thick portions provided around the first thin portion for forming lead electrodes respectively arranged corresponding to the pad electrodes of the semiconductor chip, a second thin portion provided between the plurality of first thick portions, a third thin portion provided for surrounding the plurality of first thick portions, and a second thick portion provided around the third thin portion. Accordingly, it is possible to form a concave part in the first, second and third thin portions on the upper surface side of the lead frame.
As a result, in the manufacture of the semiconductor device using such a lead frame as a wiring base member, by removing the first, second and third thin portions by etching, the circumferential portion of the mentioned concave part of the lead frame is connected to the circumferential portion of the semiconductor device including the semiconductor chip, the lead electrode, the seal resin layer, etc. provided in the concave part. Under such a condition, by extruding the semiconductor device from the under surface side of the lead frame, it is possible to separate easily the semiconductor device from the lead frame without using any cutter. It is further possible to prevent the separated portion between the lead frame and the semiconductor device 20 from being a complicated crushed configuration.
It is preferable that the first, second and third thin portions have substantially the same thickness. As a result of such arrangement, the under surface side of the lead frame can be formed into an integrated one component over the first, second and third thin portions. Therefore, in the manufacture of the semiconductor device using the lead frame as a wiring base member, when the under surface side of the lead frame comes in full contact with a lower mold and seals with the seal resin layer, the seal resin layer is shut off by the first, second and third thin portions. Consequently, there is no seal resin layer flowing in the portion where the under surface of the lead frame and the lower mold are in contact with each other, and it is possible to prevent the production of thin burr.
It is preferable that the lead frame for semiconductor device includes a plate-like body having an uneven upper surface and a plain under surface, and the plate-like body includes a first thin portion for mounting a semiconductor chip provided with a plurality of pad electrodes, a plurality of first thick portions provided around the first thin portion to form lead electrodes respectively arranged corresponding to the pad electrodes of the semiconductor chip, a second thin portion provided between the plurality of first thick portions, a third thin portion provided for surrounding the plurality of first thick portions, a second thick portion provided around the third thin portion to form an auxiliary electrode, a fourth thin portion provided around the second thick portion, and a third thick portion provided around the fourth thin portion. Accordingly, it is possible to form a concave part on the upper surface side of the lead frame in the first, second and third thin portions, and to arrange the second thick portion provided to form the auxiliary electrode around the concave part.
As a result, in the manufacture of the semiconductor device using the lead frame as a wiring base member, by removing the first, second, third and fourth thin portions by etching, the semiconductor device including the semiconductor chip, lead electrodes, seal resin layer, etc. provided in the concave part is separated from the lead frame at the circumferential portion of the semiconductor device. Consequently, it is possible to separate automatically the semiconductor device from the lead frame. Thus, it is easy to separate the semiconductor device from the lead frame without using any cutter. It is further possible to prevent the separated portion between the lead frame and the semiconductor device from being a complicated crushed configuration.
It is further preferable that the first, second, third and fourth thin portions have substantially the same thickness. As a result of such arrangement, the under surface side of the lead frame can be formed into an integrated one component over the first, second, third and fourth thin portions. Accordingly, in the manufacture of the semiconductor device using the lead frame as a wiring base member, the under surface side of the lead frame can be formed into an integrated one component over the first, second, third and fourth thin portions. Therefore, in the manufacture of the semiconductor device using the lead frame as a wiring base member, when the under surface side of the lead frame comes in full contact with a lower mold and seals with the seal resin layer, the seal resin layer is shut off by the first, second, third and fourth thin portions. Consequently, there is no seal resin layer flowing in the portion where the under surface of the lead frame and the lower mold are in contact with each other, and it is possible to prevent the production of thin burr.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.